1. Field of the Invention
This invention relates to wire coils and particularly to the packing configuration of wire coils.
2. Prior Art
When a wire is wound about an axis in order to form a coil, each revolution of the wire about the axis is referred to as a turn. Most coils have a plurality of turns which are wound adjacent to one another. In addition, coils usually have a plurality of layers of turns. That is, one layer of turns is formed by winding a plurality of turns adjacent to one another. A second layer of turns is then formed by winding the wire over the first layer of turns. The circumference of each succeeding layer of turns is greater than the preceding layer of turns. The way in which an individual turn contacts adjacent turns in a formed coil is referred to as its packing arrangement. One typical packing arrangement is known as a square lay. In this type of packing, which is shown in the drawings in FIG. 6, each interior turn of the coil is in direct contact with four other turns. This type of arrangement results in a relatively poor filling factor, i.e., there is a great deal of open space between individual turns. An arrangement which is more efficient is known as a hex winding or a perfect lay, and is shown in FIG. 7 of the drawings. In coils wound in this fashion, each interior turn is in contact with six other turns and the open space between individual turns is greatly reduced. A coil of this type is disclosed in U.S. Pat. No. 2,559,824, issued to G. J. Leland on July 10, 1951.
Although the hex packing arrangement has a relatively high filling factor, coils which employ it do not have flat sides. That is, all of the turns on either side of the coil do not lie in the same plane. This reduces the amount of wire which may be packed into a given width. This problem becomes critical when the width within which a coil must fit is extremely limited, such as is the case with printer hammers. The thickness of the coil generally must be less than 0.03 inches. Within this thickness, it is imperative that as much wire as possible be wrapped in order to form a coil having the maximum flux density for a given current. Within a given space, the coil having the highest packing density will give the best performance.
One method which may be utilized to aid in the formation of coils is to apply a packing pressure to the peripheral surface of a coil as it is being wound. Such an arrangement is illustrated in U.S. Pat. No. 1,383,186, issued to C. A. Brink on June 28, 1921. By utilizing this type of packing pressure, a tight pack is assured.